Apparatus and process for melting material of high melting point



Nov. 26, 1957 J. s. BALLANTINE 2y814550 APPARATUS AND PR'oCEss PoRMELTING yMATERIAL oP HIGH MELTING POINT Filed April 2s, 1954 lJima@ d H370 CQ/, g Z6 Fg@ ATTORNEYS.

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APPARATUS AND PROCESS FOR MELTING MATERIAL F HHGH MELTING POINT `lamesS. Ballantine, Absecon, N. J.

Application April 23, 1954, Serial No. 425,273

Claims. (Cl. 75-84) The present invention relates to the melting anddesirably also purifying of materials of high melting point, especiallymetallic zirconium, titanium and hafnium.

A purpose of the invention is to melt individual particles of highmelting point material free from contamination by heating the particlesby a preheated gas while the particles are free in the gas, ldesirablysupplementing by heat additionally applied in the chamber containing thegas.

A further purpose is to introduce the `gas into the chamber in -anupward direction or in a swirling direction, or preferably in an upwardswirling direction, and thus retard the fall of the particles anddesirably also apply centrifugal force to them.

A further purpose is to meter the particles as they are introduced andseal against escape of inert gas, introducing the particles at a rate solow that the particles remain free in the gas.

A further purpose is to employ particles of preferably uniform size andof sufficient size to drop in the gas.

A further purpose is to introduce the particles at the outside of thechamber where they will be most effectively picked up by the swirl.

A further purpose is to preheat the gas in a chamber which preferablyconsists of the material to be melted so as to minimize the possibilityof contamination.

A further purpose is to eliminate impurities as the particles are heatedand melted and particularly to carry off magnesium and magnesiumchloride from zirconium, titanium and hafnium.

A further purpose is to introduce argon along with helium as the inertgas and thereby facilitate the carrying ofi of impurities by the gas.

A further purpose is to carry the particles, after they have been heatedby the inert gas, through a booster chamber preferably located below thechamber in which the particles are rst heated, the booster chamber beingmaintained at a temperature substantially above the melting point of thematerial to be melted.

A further purpose is to drop the particles through the booster chamberand desirably also to have the particles swirl in the booster chamber.

A further purpose is to heat the booster chamber by a resistance arc incarbon and desirably to protect the arc against the molten metal andmetal vapor by a refractory wall of the booster chamber, preferably alsoof carbon, and to avoid contamination by dropping the particles throughthe booster chamber, and thus minimising contact with the chamber wall.

A further purpose is to deposit the molten particles on a continuonscasting desirably immediately below the booster chamber and preferablyto cool the continuous casting in an atmosphere of inert gas.

A further purpose is to introduce alloy into the particles immediatelybefore they solidify in the continuous casting.

Further purposes appear in the specification and in the claims.

In the drawings l have chosen to illustrate one only of the numerousembodiments in which my invention may appear, selecting the form shownfromv the standpoints of convenience in illustration, satisfactoryoperation and clear demonstration of the principles involved.

Figure 1 is a diagrammatic central vertical section of mechanism inaccordance with the invention.

Figure 2 is a fragmentary enlargement of the upper portion of Figure 1.

Figure 3 is a section on the line 3 3 of Figure 2.

Figure 4 is an axial section through one form of gas preheater inaccordance with the invention.

Describing in illustration but not in limitation and referring to thedrawing:

The present invention is concerned with the melting and purifying ofmaterials of high melting point, especially zirconium and also primarilytitanium and hafnium. The principles of the invention in its broaderform are also applicable to the melting and purifying of otherrefractory metals, for example, tungsten, iridium and the noble metalssuch as platinum, and also to the melting and purifying of highlyrefractory materials, such as refractory carbides, like the carbides oftungsten, boron and titanium, and refractory oxides such as zirconia,chromium oxide, magnesia and alumina.

Metallic zirconium is commonly obtained by the Krole process, whichproduces a sponge containing impurities, especially magnesium chloride,and secondarily iron, other metallic oxides and nitrogen. The usualtechnique for initial purifying is to vacuum distill. Various grades ofpartially purified zirconium are obtained by vacuum distillation,depending upon the position of the material in the condenser, and theseare blended to obtain the purity desired, the most impure material beingsent back for reprocessing.

Great difliculty has been encountered in melting zirconium to obtainingots of high purity.

Because of its high melting point, about 3555 F., zirconium cannot bemelted in most refractories, and the use of carbon refractory isprohibited by the fact that carbon is one of the most objectionableimpurities in zirconium. Other impurities which are quite objectionablefor their effect on rolling are magnesium, magnesium chloride, yandnitrogen.

By the present invention it is possible to obtain a very high purity ofmolten zirconium or other molten material, eliminating impurities suchas magnesium and magnesium chloride and avoiding substantial pickup ofimpurities such as carbon and nitrogen.

In accordance with the present invention, the material to be melted andpurified, for example, zirconium sponge, is introduced in the form ofparticles, preferably of uniform size, and suitably of the order of l/to 1A inch in size, although larger or smaller particles can be used aslong as the particles are small enough to be retarded by the gas andlarge enough to prevent them from becoming completely air-borne and frombeing carried out of the furnace with the gas. lf the particles `consistof zirconium and are badly contaminated with magnesium chloride, it ispossible to remove a large percentage of the magnesium chloride byleaching.

The particles 20 are charged into a hopper 21 at the top of the furnaceand the discharge of the particles from the hopper is metered, While atthe same time a gas lock is provided, suitably by cylindrical housing 22at the bottorn of the hopper which contains a cylindrical rotor 23having metering pockets 24 in its periphery. The pockets are largeenough to receive a predetermined charge of particles to be melted asthe rotor turns, for example at a controlled speed under the action of asuitable drive.

The metering is regulated so that the particles will not clog thefurnace but will behave as individually free particles as they passthrough the furnace and will in the main remain separate in the gas. Itshould be noted that the furnace chamber is not charged full ofparticles. Any other suitable metering means and gas lock may be used4The particles drop from the metering device into a charge opening 2S atthe bottom of the hopper and are preferably diverted to the outside by abell 26 supported by a spider 27.

The particles drop into an initial heating and purifying furnace 218having an interior suitably vertical preferably cylindrical chamber 30formed by a vertical tube 31 of a suitable refractory, preferablyzirconia in the case of meltA ing zirconium.

Inert gas which in the case of zirconium, titanium, hafnium, tungsten oriridium, will be argon, xenon, neon, krypton or helium or a mix-ture ofthe same, is introduced suitably from compressed cylinders or othercontainers through pipe 32 of preheater 33 consisting of a housing 34and internal helical Walls 35 forming a helical internal passage 36. Thehousing 34 and the helical walls .35 are desirably made of the materialto Vbe melted, or its oxide, so that where the metal to be melted iszirconium the gas as it is heated will come in contact only withzirconium or zirconia at this stage. The housing and the helical Wallsare heated by an electric inductor 37 suitably carrying intermediate orhigh frequency alternating electric current and desirably water cooled.The housing and the inductor is surrounded by heat insulation 38. Thespace surrounding the housing is desirably lled with inert gas by aninlet connection 40 and an outlet connection 41.

Any other suitable means of heating the inert gas may be used. The inertgas is preferably heated in the preheater to a temperature slightlybelow the melting point of the material being melted. The preheatedinert gas passes through pipe 42, preferably also composed of the samemetal which is being melted, into a plenum chamber 43 which is formedaround the refractory tube 31. The plenum chamber on the outside has arefractory wall 44, which may be formed, depending upon the metal beingmelted, of carbon or a carbide such as zirconium, titanium or hafniumcarbide when zirconium is being melted, or a refractory oxide such aszirconia, and is an electric conductor at the operating temperature, andthis is surrounded by induct-or coil 45 of an electric inductionfurnace, suitably at intermediate or high frequency of alternatingcurrent, which develops additional heat in the plenum chamber to adjustthe temperature of the inert gas to a temperature substantially that ofthe melting point of the material to be melted, or slightly above thesame. It will be understood that the carbon refractory 44 is surroundedby an outer jacket. not shown, containing i inert gas to protect againstoxidation.

From the plenum chamber the inert gas is projected through jet openings46 into the furnace chamber 30. The jet openings will be preferablyconsiderably more numerus than those shown, extending diagonallyupwardly and preferably also tangentially to produce a whirl of inertgas at very high temperature in the chamber 30. This Whirl is movingupward. The pressure of lthe inert gas will suitably be of the order ofl to 3() p. s. i. gage at room temperature, but of course at theelevated temperature the gas is at much higher pressure in the plenumchamber and in the furnace chamber 30.

The particles of material to be melted drop into the chamber 30,preferably near the outside and their fall is retarded by the upward owof the gas and also by the whirling action. This whirling action causescentrifugal force which is very important in eliminating impurities asthe particles melt. It is possible actually to see impurities separateat this stage. In the case of zirconium, impurities such as magnesiumand magnesium chloride pass out with the inert gas through flue 47 atthe top. The inert gas and impurities are preferably carried to a con--denser not shown which separates the impurities, and the inert gas ispreferably collected, repurified and reused.

The preferred composition of the inert gas is a mixture of helium withabout 25 percent by volume of argon. lt has been found that argon ishelpful in aiding the separation of impurities from metal such aszirconium, titanium, and hafnium, and it is believed that argon in thecontent of 5 to 50 percent by volume of the total gas with the balancehelium or some other monatomic inert gas is desirable. Nitrogen shouldat all costs be avoided with zirconium, titanium or hafnium. Whenmelting zirconium, the gas entering the plenum chamber is preferably ata 4temperature of about 3000" F. and is heated in the plenum chamber toa temperature of about 4000" F. The particular temperature of coursewill vary with different materials being melted, gas pressure and grainsize of the particles.

Magnesium chloride begins to evolve from zirconium at a temperature ofabout 1300 to 2600 F. The ltime taken by the particle to fall throughthe chamber 3l? is preferably about 5 to l0 seconds, due to theretardation from the upward flow of the gas and due to the centrifugalforce which makes it take a long path. The surface agitation, thecentrifugal force and the time of exposure at high temperature are allimportant factors in eliminating impurities such as magnesium, magnesiumchloride, nitrogen and iron from zirconium or the like.

While it will be evident that a succession of whirling gas chambers ofthe character of the chamber 30 can be used, it is preferred toaccomplish the melting by the use of a booster chamber which addsadditional heat to the already melted or nearly melted particles whichleave the bottom of the chamber 30. The booster chamber is desirably azone of very high temperature indeed, through which the particles maydrop relatively rapidly. It is ordinarily placed immediately below thechamber 30. As best seen in Figure l, a booster chamber 48 suitably ofcylindrical form is placed beneath the chamber 30, and has a suitablyvertical tubular refractory wall 50. The refractory Wall 50 is desirablyof carbon in the case lof melting zirconium, although in suitable casesother refractories may be used such as high melting point carbides likethe carbides of zirconium, titanium and hafnium. The temperatureprevailing in the chamber 48 is preferably in the range of 6000 to 8000"F. (the larger the particle size, the higher the temperature) whenmelting zirconium or similar materials, and this temperature may beobtained in any suitable Way, but preferably from a carbon resistancearc as disclosed in detail in my application Serial No. 289,373, tiledOctober 30, 1953, for Electric Arc Resistance Furnace. In a carbonresistance arc furnace it is very important to maintain the stability ofthe arc by protecting it from metal vapor and molten metal of theparticles dropping through the chamber 4S, and therefore the refractoryWall 50 forms a closed envelope inside the booster furnace 51.

The booster furnace 51 preferably comprises an inner series ofintertitting carbon arcing rings 52 engaged at the top by a carbonresistor contact ring 53 connected to a metallic terminal 54 and engagedat the bottom by a carbon resistor contact ring 55 engaged by metallicterminal 56. The inner set of arcing rings 52 is preferably surroundedby a relatively spaced -outer set of interlocking carbon arcing rings 57connecting at the top by a carbon resistance contact ring 58 engaged bya metallic terminal 60 and connecting at the 'bott-om with a carbonresistor contact ring 61 engaged by metallic terminal 62. Insulatingspacers are provided at 63 and 64 to separate the inner and outer setsof carbon resistance arcing elements. The entire resistance arc furnaceis surrounded by an envelope of inert gas in a container not shown.

As the particles of material to be melted drop through the boosterchamber 48 they are still whirling from the action of the gas and ofcourse the chamber 48 is filled with inert gas. The particles completetheir melting if vthey are not already melted and preferably become veryhighly superheated in the booster chamber 4S so that they are extremelyuid indeed by the time they reach the bottom of this chamber. The lastvaporizable 'impurities pass off under very high superheat aided by thewhirling action in the booster furnace.

An important aspect of this invention is that the particles drop quicklythrough the chamber 48 without any intimate or prolonged contact withthe carbon refractory wall, since the chamber wall has no projectionsinto the path of the particles, being of uniform cross section. Thus itis possible to secure a very low carbon content in the resulting ingotnotwithstanding the carbon refractory wall at this point. This is veryimportant with zirconium where a substantial carbon content may make themetal unrollable.

It will be understood that where desired an electric induction furnacemay be substituted instead o f the Ballantine carbon resistance arc.

When it is desired to make an ingot, the molten particles are depositedat 65 in a continuous casting mechanism 66 at the top of a continuouslyforming ingot 67 which is withdrawn by motor 68 and worm 70 engagingworm wheel 71 which forms a nut on screw 72 connected to the ingot, thenut being held by a bearing not shown. The solidifying collar '73 of thecontinuous casting appara-tus, suitably of copper or the like, surroundsthe ingot at the point of solidication, and is water-cooled, introducingwater at 74 and withdrawing it at 74. The solidifying collar has areverse taper 75 (in the direction of withdrawal) to aid in withdrawingthe ingot.

in order to protect the ingot against oxidation, it is surrounded by ajacket 76 below the cooler having inert gas at 77 provided with a gastight seal at 78 against the ingot. The inert gas is brought in by pipe77 and withdrawn by pipe 772.

The very high superheat is important in obtaining a homogeneous solidingot free from blow holes. There is so much superheat in each globuleas it comes down that it melts the adjoining metal below it and forms airm and continuous metallic bond as it solidies.

In some cases it is desired to insert alloying ingredients, andprovision is made for this by a tube 80 extending into the chamber 48immediately above the point of solidification and directing a stream ofalloying ingredients on the top of the ingot. It has been found thateven relatively volatile alloying ingredients can be introduced at thispoint, and although alloy loss is suffered, it is not prohibitive. Forexample such materials as tin have been alloyed with zirconium by thismethod, the tin particles being introduced among the depositing globulesas they are still molten and beginning to solidify.

By way of example, in experiments conducted using the process andfurnace of the invention, the chamber 30 has been slightly smaller than3" in inside diameter and from 24 to 36l long and chamber 48 has beenabout 3 in inside diameter and approximately 6 long.

The gas has been fed to the chamber 30 at the rate of approximately 150cubic feet per hour, measured at standard conditions of temperature andpressure.

In melting heavy metals (having specific gravity greater than 12) therate of feed to the furnace has been about 2O pounds per hour. Withmetals having specific gravity below 12, the rate of feed has beenconsiderably higher of the order of 75 pounds per hour.

It will be evident that one of the very important aspects of theinvention is the heating and melting of the particles as they areiloating in or slowly dropping through the inert gas.

It will further be evident that another important aspect is the whirlingaction which greatly assists both in heating and also in centrifugalelimination of impurities.

lt will further be evident that an important aspect of the invention isdropping of the particles past a wall of carbon refractory withoutholding the particles in intimate contact with the Wall so thatcontamination will be minimized.

lt will further be evident that an important aspect of the invention isthe depositing of very highly superheated globules of molten metal onthe continuous casting so that each globule will melt adjoining metalbelow it and assure uniformity.

In View of my invention and disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain all or part of the benefits of myinvention without copying the process and apparatus shown, and I,therefore, claim all such insofar as they fall Within the reasonablespirit and scope of my claims.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. The process of melting a high melting material free fromcontamination, which comprises preheating inert gas in a separatepreheating chamber, metering particles of the material to b e melted ata rate suiciently low so that the particles will pass through a firstfurnace chamber individually, introducing the metered particles of thematerial to be melted near the top of the first furnace chamber, passingthe inert gas from the preheating chamber into the first furnace chamberand separating the particles by the gas in the furnace chamber andthereby retarding the downward tlow of the particles while heating theindividual particles of the material to be melted by the sensible heatof the inert gas, additionally heating the rst furnace chamber, droppingthe particles through the irst furnace chamber into a second boosterfurnace chamber below the first, and also containing the inert gas, andin the booster chamber heating the particles to a temperaturesubstantially above the melting point of the material to be melted.

2. The process according to claim 1, which comprises introducing theinert gas into the first furnace chamber in a swirl direction andcarrying the particles with the inert gas in centrifugal motion.

3. The process according to claim 1, which comprises introducing theinert gas into the rst furnace chamber in an upward direction anddropping the particles through the inert gas while retarding the fall ofthe particles by the inert gas.

4. The process according to claim l, in which the particles are ofsubstantially uniform size.

5. The process according to claim 1, which comprises preheating theinert gas in the preheating chamber while in contact with material ofthe same character as the material to be melted.

6. The process according to claim l, in which the material to be meltedis a metal of a class consisting of zirconium, titanium, hafnium,iridium and tungsten.

7. The process according to claim 1, which comprises swirling theparticles as they drop through the booster chamber.

8. The process according to claim l, in which the booster chamber iscomposed of carbon, which comprises dropping the particles through thebooster chamber and thereby avoiding contamination with the carbon.

9. The process according to claim 1, which comprises heating the boosterchamber by resistance arc in carbon, protecting the arc against themolten metal and metal vapor and dropping the particles through thebooster chamber and thereby avoiding contamination with the boosterchamber wall.

10. A furnace for melting materials of high melting point, comprising apreheater for preheating a stream of inert gas, a first vertical furnacechamber, means for metering particles to be melted and introducing theparticles at the top of the first furnace chamber at a rate so low thatthe particles pass through the first furnace chamber individually, meansfor introducing the preheated inert gas into said first furnace chamberand thereby heating the individual particles of material to be meltedwhile they are free in the inert gas, means for additionally heating thefirst furnace chamber, a second booster furnace chamber vertically belowthe first furnace chamber and means for heating the booster furnacechamber to a temperature substantially above the melting point of thematerial to be melted.

11. A furnace according to claim 10, in -which the means for introducingthe preheated gas into the first furnace chamber comprises upwardlydirected jets.

12. A furnace according to claim 10, in which the means for introducingthe inert gas into the first furnace chamber comprises circumferentiallyland upwardly directed jets.

13. A furnace according to claim 10, in which the wall of the preheaterfor the inert gas is composed of the same material as the material beingmelted.

14. A furnace according to claim 10, in which the means for heating thebooster chamber consists of a resistance arc in carbon.

15. A furnace according to claim 10, in which the booster chamber has acarbon refractory inner wall and the means for heating the boosterchamber consists of a resistance arc in carbon surrounding the carbonrefractory wall.

CII

References Cited in the tile of this patent UNITED STATES PATENTS MooreSept. 15, Schauer July 10, Junghans Dec. 15, Brown Apr. 1, Witt Apr. 7,Herres lune 2, Urban July 20, Lewis June 21,

FOREIGN PATENTS Great Britain Jau. 30,

OTHER REFERENCES Transactions of The Electrochemical Society, page 163,vol. 96, No. 3, September 1949.

1. THE PROCESS OF MELTING A HIGH MELTING MATERIAL FREEE FROMCONTAMINATION, WHICH COMPRISES PREHEATING INERT GAS IN A SEPARATEPREHEATING CHAMBER, METERING PARTICLES OF THE MATERIAL TO BE MELTED AT ARATE SUFFICIENTLY LOW SO THAT THE PARTICLES WILL PASS THROUGH A FIRSTFURNACEE CHAMBER INDIVIDUALLY, INTRODUCING THE METERED PARTICLESS OF THEMATERIAL TO BE MELTED NEAR THE TOP OF THE FIRST FURNACE CHAMBER, PASSINGTHE INERT GAS FROM THE PREHEATING CHAMBER INTO THE FIRST FURNACE CHAMBERAND SEPARATING THE PARTICLES BY THE GAS IN THE FURNACE CHAMBER ANDDTHEREBY RETARDING THE DOWNWARD FLOW OF THE PARTICLES WHILE BY THESENSIBLE HEAT OF THE INERT GAS, ADDITIONALLY HEATINGG THE FIRST FURNACECHAMBER, DROPPING THE PARTICLES THROUGHH THE FIRST FURNACE CHAMBER INTOA SECOND BOOSTER FURNACE GAS, AND IN THE BOOSTER CHAMBER HEATING THEPARTICLES TO A TEMPERATURE SUBSTANTIALLY ABOVE THE MELTING POINT OF THEMATERIAL TO BE MELTED.